Onshore Petroleum Project

• Project description
• Project objectives
• Target areas
• Project outcomes
• Project outputs

Project description

Australia hosts numerous producing hydrocarbon provinces most of which are located offshore. Only the Cooper/Eromanga region operates as a major onshore oil and gas producer delivering hydrocarbons to markets in Queensland, New South Wales and South Australia. Although many new significant gas discoveries have been made in recent years, it is widely acknowledged that Australia’s oil production has been in steady decline since the late 1990s and that increasing amounts of liquid hydrocarbons are needed to satisfy the continued demand.

In the context of declining oil supply, the Australian Government provided Geoscience Australia with the funding for the New Petroleum Program (2003-2007) and the Energy Security Program (2007-2011). The purpose of these programs is to supply pre-competitive data and information to stimulate exploration in under-explored areas. While “New Petroleum” was exclusively focussed on under-explored offshore areas, “Energy Security” targets both, onshore and offshore frontier basins. In addition to petroleum, it also includes onshore assessments of uranium, thorium, and geothermal resources. As part of this initiative, the Onshore Petroleum Project focuses on those sedimentary basins that are perceived to be prospective for oil and gas, as indicated by previously recorded hydrocarbon shows. Recognising the under-explored status of such prospective regions, a staged program of new data acquisition is currently underway.

Project objectives

Taking an innovative approach, project work includes the utilisation of new regional potential field data and the acquisition of several deep seismic surveys in order to image basement features that exerted a controlling influence on basin architecture and tectonic evolution. Under guidelines outlined in the National Geoscience Agreement, Geoscience Australia has consulted with the States and Northern Territory to agree upon a deep seismic acquisition program with specific line kilometres devoted to petroleum provinces. Two regional deep seismic surveys will be acquired over Neoproterozoic and Palaeozoic basin provinces that are known to host active petroleum systems. Seismic signals down to 16 seconds TWT will be recorded and processed allowing the entire upper crust to be imaged. With respect to hydrocarbon occurrences, basinal sections (6-8 seconds TWT) will be delineated permitting the interpretation of architectural relationships with basement terranes, prevailing structural styles and the effects of tectonic overprints on the basin-fill sequences. This latter aspect will highlight the potential for hydrocarbon preservation subsequent to orogenic phases.

Figure 1 Map of Australian continent showing distribution of onshore sedimentary basins
(Click on image for larger version)

Target areas

The first seismic survey with a petroleum focus was acquired in March 2008 over the Rankin Springs and Yathong troughs of the Darling Basin in western New South Wales. The troughs represent extensive structural lows in which basement depths exceed 3,500 m and in which basin-fill includes Devonian and Permo-Triassic sediments. These sequences potentially contain several source rock intervals and are therefore deemed to be highly prospective with respect to petroleum and possibly coal seam gas. The survey will fill the existing data gap and enable the preliminary imaging of source rock occurrences, stratigraphy, and structure of the sedimentary fill of these troughs.

The Gawler-Curnamona-Arrowie seismic survey is scheduled for April 2008 and will mainly evaluate the geothermal and uranium potential in central South Australia’s basement provinces. A distinct petroleum component of this survey is provided by the southern section of the Arrowie Basin, where oil shows were recorded in Cambrian sediments.

Another regional survey, planned for South Australia and the southern Northern Territory later in 2008, will comprise a seismic traverse across the eastern Officer Basin crossing the Musgrave Block and terminating in the Amadeus Basin well north of the southern basin margin. The Officer Basin is Neoproterozoic to Devonian in age and, based on numerous oil shows, is known to host four petroleum systems. The most prolific of these is related to a carbonate/playa sequence within the Marla overthrust where thick salt horizons could provide an effective regional seal.

The Amadeus Basin, like the Officer Basin, contains a Neoproterozoic to Late Devonian sedimentary section that reaches a maximum thickness of about 17 km. Five petroleum systems have been identified and the Palm Valley gas field and the Mereenie oil and gas field produce from Ordovician reservoirs providing energy to consumers in the Northern Territory. Recent analyses of live oil bleeds collected from the Finke-1 well suggest that a 50 m oil column is preserved at this location. It has been concluded that this oil was derived from Neoproterozoic sources, confirming that these geologically old sediments are indeed capable of generating petroleum.

A further petroleum-focussed survey, currently scheduled for the 2009/2010 financial year, will traverse the Kidson Sub-basin, a southern depocentre of the onshore Canning Basin, WA. The sub-basin contains up to 7 km of Early Ordovician to Cretaceous sediments representing the most complete stratigraphy in the region. This onshore frontier area is sparsely explored and only minor oil and gas shows were recorded in some of the 13 wells drilled to date. Petroleum systems in the area can be subdivided into sub-salt and supra-salt plays. Excellent Ordovician source rock intervals are known to exist in the region and may lie within the oil window at shallow depths along the basin margin.

Project outcomes

Modern seismic data provide greatly improved imagery of the subsurface leading to a better understanding of basin fill sequences and geological structures in the basin. From this the likely distribution of source rocks, their maturity levels and their preservation potential may be interpreted. A key result will be to gain insights into the likely effects of regional orogenic events on the hydrocarbon-bearing strata. The new data will be made available to industry to assist current and future explorers in their efforts to unlock the untapped hydrocarbon potential in these frontier regions. It is anticipated that the results of these surveys will drive a new exploration phase in onshore Australia and will lead to a synthesis of the onshore hydrocarbon potential.

Project outputs

Onshore data acquisition:

Planning, scoping and acquisition of geophysical/geological data in the Central Australian region (greater Cooper/Eromanga, Amadeus and southern Canning regions) in order to delineate structural linkages between basement and basins and geological controls on the presence and operation of hydrocarbon systems and other commodities such as geothermal energy.

Pilot studies on the distribution of energy commodities:

A preliminary geological assessment of the occurrence and distribution of onshore oil and gas. The results will be used to select areas for future exploration acreage release.